The present invention relates to diagnostic and therapeutic methods and apparatus, particularly to those which use bioelectrical characteristics of a human body as primary data. Heretofore, medical instruments and methods employed have been processing a variety of electrical signals due to bioelectrical and biochemical activities of a human body, such as brain waves (EEG), skin potentials, impulses related to general muscle activity (EMG), or specifically, heart muscle activity (EKG), and a variety of other potentials from other areas of the human body. The relative values of the potentials (voltages) are very small--for constant or slowly changing potentials, the value is about tens microvolts and for fast changing ones (impulses) the amplitude is less than 250 microvolts. The widest applications have been achieved by those devices which have processed changing potentials--impulses, or electrical waves. Some of the instruments and methods measure passive characteristics of the body, such as an impedance (skin resistance or resistance between two given points). In the last case, to obtain data (either current or resistance), a source of external voltage must be applied, but this also affects inner body structures in unpredictable ways, so that the informative level of the data is low.